Calculator
Formula used
Power method: kWh/day = (Watts * (Duty% / 100) * Hours/day) / 1000
Label methods: kWh/day = Annual kWh / 365 or use your known daily value.
The calculator adds defrost energy (kWh/month / 30), then applies usage and season multipliers. Cost is kWh * rate for each time period.
How to use this calculator
- Choose an input method: watts, daily kWh, or annual kWh.
- Enter your electricity rate and fridge values from the label.
- Adjust multipliers for shed heat and harvest loading.
- Click Estimate Cost to see results above the form.
- Download CSV or PDF to share or track changes.
Example data table
| Scenario | Input method | Energy (kWh/day) | Rate (per kWh) | Est. Cost / Month |
|---|---|---|---|---|
| Garden shed, warm summer | 150W, 35% duty, 24h, season 1.15 | ~1.45 | 55 | ~2,393 |
| Seed storage, stable indoor | Known kWh/day = 1.10, normal multipliers | 1.10 | 55 | 1,815 |
| Labelled appliance | Annual kWh = 420, average multipliers | ~1.15 | 55 | ~1,898 |
Why fridge energy varies with harvest loads
When you chill freshly picked produce, the fridge must remove field heat before it can hold a steady setpoint. Warm crates, wet greens, and uncovered pans dump moisture and heat into the cabinet, forcing longer compressor runs. Frequent door openings during washing and packing add another surge. The usage multiplier models these patterns so estimates match busy harvest weeks, not just quiet days. Pre-cooling in shade and using lids can cut load quickly.
Turning watts and duty cycle into daily kWh
If you only know running watts, duty cycle is the missing piece. A compressor that draws 150 watts but runs 35% of the day uses about 1.26 kWh/day at 24 hours. Older units may spike higher at startup, while inverter models vary smoothly. This calculator converts watts and runtime into daily kWh and then scales to weekly, monthly, and yearly costs.
Season and ambient temperature effects
Fridges placed in garages, sheds, or hot kitchens work harder because heat leaks through the cabinet faster and the condenser rejects heat less efficiently. Poor airflow behind the unit can raise energy use noticeably. A seasonal multiplier represents hotter months, dust buildup, or direct sun. In a cool shaded room, a lower multiplier helps estimate savings from better placement and ventilation.
Defrost cycles and maintenance penalties
Frost buildup acts like insulation on the evaporator and reduces airflow, so the compressor stays on longer to reach target temperatures. Auto defrost models also add energy during heater cycles, which can matter when humidity is high from produce. The defrost kWh/month field captures this overhead. Regular coil cleaning, leveling doors, and replacing worn gaskets reduce cycling and stabilize storage conditions.
Using results for budgets and quick decisions
Once you have kWh/day, scaling is straightforward: multiply by 30 for a month and by your electricity rate for cost. Use the results table to compare a baseline setup versus changes such as raising the set temperature slightly, leaving headspace for airflow, or batching door openings after sorting. Add notes to track experiments, then export CSV or PDF to share with helpers. For seasonal planning, run a summer and winter case side by side.
FAQs
1) What duty cycle should I start with?
Most household fridges average 25–45% in typical indoor conditions. Start at 35%, then adjust using a plug-in energy meter or by matching your bill and label estimates.
2) I have an annual kWh label. Is it more accurate?
Often yes, because it reflects standardized testing. Still, real-world factors like room heat, door openings, and warm produce loads can raise usage. Apply the multipliers to bridge that gap.
3) Why does my cost change so much in summer?
Higher ambient temperatures increase heat gain through the cabinet and reduce condenser efficiency. Poor ventilation in a shed or garage makes this worse. Use the seasonal multiplier to represent these conditions.
4) How can I reduce energy without hurting produce quality?
Cool produce in the shade first, avoid overpacking, leave space for airflow, and keep gaskets clean. Group door openings, and store watery crops in sealed containers to reduce moisture and frost.
5) Does a second “garden fridge” always cost less than spoilage?
It depends on rate, kWh/day, and the value of saved produce. Compare monthly energy cost from this calculator to the average monthly value of avoided waste.
6) What if I measured kWh/day with a smart plug?
Select “Known kWh per day” and enter the average from several days. Include a harvest day and a quiet day so your estimate reflects your real garden routine.